Bridging the gap

Laser welding may not be able to replace every conventional welding process, but it offers plenty of advantages in applications where it can be used. Firmly established in the automotive industry for joining processes, including dissimilar metals, laser welding continues to be more widely applied, moving into the oil and gas, aerospace, defense and medical industries.

For medical parts, it is clear that some parts are so tiny they can only be joined by laser welding. For aerospace parts, laser welding works well with the various alloys used, such as titanium, and doesn’t create any microstructure issues. For defense applications, laser welding provides the deeper penetration required for the thicker materials used.

“In laser welding, the energy is transferred through a very small beam,” says Masoud Harooni, product manager for laser welding at Trumpf Inc. “Because the energy is so concentrated, we get very deep penetration. And because the heat is very concentrated, there is less heat input in the part compared to traditional welding.”

Examples of a joint configuration welded with various methods. From bottom to top: unwelded; manual MAG weld; FusionLine weld where there was no need for part redesign; laser weld after being redesigned for laser processing.

Best benefits

All of this leads to numerous advantages of laser welding over conventional techniques. Less heat input means minimal metal distortion and, therefore, less rework on the part. High-quality weld seams mean grinding or other surface work is not required.

Also, less heat input means a smaller heat-affected zone, which is another issue with traditional welding. This leads to less metallurgical issues, such as cracking.

“Overall, there is an investment with laser welding but the benefits outweigh the costs in most cases,” Harooni says. “When you break it down for an individual job, you’ll find you don’t need to spend 20 min. grinding a part, for example. Or, there will be no distortion in the part. Or, you can go 120 ipm, for example, instead of the 20 ipm with MIG welding.”

However, laser welding has one big disadvantage and that is the narrow laser beam cannot weld across large gaps. That’s not to say gaps cannot be laser welded. But the best way to address these gaps, according to Harooni, is to redesign the parts to eliminate them.

“Joint configuration can be redesigned to make it suitable for laser welding,” he says. “We make it easier for the laser to join two base metals together.”

Just add wire

However, another option for bridging gaps is now available – adding wire.

For joints that can’t be reconfigured without gaps, the FusionLine laser welding process using welding wire can weld gaps up to 1 mm wide. That makes it possible to use laser welding on many parts designed for conventional welding methods.

The TruLaser Weld 5000 features a rotary module that rotates the shielding gas nozzle continuously around the optics. The robot does not need to reorient itself.

With FusionLine, wire is added to the joint to actually bridge the gap. The wire and base material are melted and fusioned by the laser. From one side of the laser, the wire is fed to the molten pool. From the other side comes the same shielding gas used for the laser welding. Similar to MIG welding, the wire is fed to the laser head with a wire feeder.

“The key is this is not arc welding and not laser hybrid arc welding,” Harooni says. “It is laser welding assisted with wire. It is adding extra mass to the material that is fused into the gap. Hybrid laser welding combines gas metal arc welding with laser welding.”

More options

FusionLine is featured as an option on the TruLaser Weld 5000 automated laser welding system. Users can switch between FusionLine and the typical laser welding with no need to reset the machine. Users can also switch between the two on the same part, even halfway through processing it.

The TruLaser system also offers a range of loading and unloading solutions, including a rotational changer to load and unload parts manually or automatically while welding is occurring inside the machine, decreasing cycle times.

For the flexibility needed for high a variation of parts, lower volumes, Trumpf offers modular fixturing to weld those small lot sizes.

And before the welding itself begins, the TeachLine option helps with repeatability. The TeachLine sensor system detects variations and counters them to achieve dimensional precision for weld seams.

“Say there is a slight difference with your fixture from part to part,” Harooni says. “TeachLine would detect edges or corners and then it would weld the seam that is actually the right one. It compensates for slight variations that you might have in the parts.”

The rotary module for shielding gas guidance provides excellent parts accessibility. The module rotates the shielding gas nozzle around the optics instead of having to move the whole laser head and robot. The result is faster welding times and simplified programming and fixturing design. Despite all these advantages, Harooni notes some companies are still hesitant about introducing laser welding to their operations.

“I see people familiar with more traditional welding in industries such as agriculture that don’t understand how that tiny laser beam can weld large, thick parts at the same strength as MIG welding,” he says. “But there are two good reasons. Laser welding has better mechanical properties and microstructures. And, the high power density results in higher penetration and higher strength.

“It is time for industry to understand that laser welding is not just cosmetic, but affects the structure as well,” he concludes. “The cars of today are being laser welded, so that should tell you something. It is a good weld.”